Catalytic hydrogenation of carbon monoxide with indirect heat exchange cooling



Aprll 3, 195e Q. DORSCHNER 2,740,803

CATALYTIC HYDROGENATION OF CARBON MONOXIDE WITH INDIRECT HEAT EXCHANGECOOLING Filed Jan. 9. 1951 United States Pate CATLYTIC HYDROGENATION OFCARBON MONOXIDE WITH INDIRECT HEAT EX- CHANGE COOLING Oskar Dorsehner,Bad Homburg, Germany, assigner to Ruhrchemie Aktiengesellschaft,Oberhausen-Holten, Germany, and Lurgi Gesellschaft fr Warmetechnii; m.b. H., Frankfurt am Main, Germany, two German corporations ApplicationJanuary 9, 1951, Serial No. 205,076

Claims priority, application Germany January 19, 195th 6 Claims. (Cl.2641-449) This invention relates to temperature-gradient in connectionwith uniformly boiling coolants.

The catalytic treatment of gases, containing carbon monoxide andhydrogen, into higher hydrocarbons, may be conducted so that larger orsmaller quantities of hydrocarbon derivatives containing oxygen areobtained, e. g. alcohols, fatty acids or the like. When proceeding inthe conventional manner using the contact process with rigidly arrangedcatalysts, only quantities of 0.15 to 0.2 ton of the higher hydrocarbonsand, under certain conditions other compounds containing oxygen areobtained per m3 of catalyst per day. In the above method the catalystsare placed in thin layers of 7.5 to 10 mm. thickness between cooled heateXchange surfaces (laminated ovens) or in tubes of 10-15 mm. diameter,or in the annular space between two telescoped tubes with a distance ofabout 10 mm. between the inner and outer tube. The cooling process inthese methods had to be made especially eifective in order to dissipatethe generated reaction heat. Usually this was done by using boilingwater under pressure. The use of larger contact layers was impossiblebecause this would have produced excessive temperatures of the contactlayers which would have resulted in side reactions, such as formation oflarge quantities of methane, separation of carbon and damage to thecatalysts. The cooling with boiling water under pressure resulted innearly constant reaction temperatures of the gases passing through thecontact oven.

One object of this invention is increasing the yield in the synthesis ofhigher hydrocarbons using uniformly boiling coolants in the contactprocess. This and further objects will become apparent from thefollowing description read in conjunction with the drawings in which:

Fig. 1 shows apparatus which can be used for the process according tothe invention.

Fig. 2 shows another form of a contact tube which may be used inaccordance with the invention.

Fig. 3 illustrates another form of a contact tube.

Fig. 4 is a vertical cross section of a contact oven with a suspendedcontact.

Fig. 5 shows another form of construction of the apparatus which may beused for the process in accordance with the invention.

Fig. 6 shows still another form of the apparatus which may be used forthe process according to the invention.

It has now been found according to the invention that when using highgas velocities of more than .5 and suitably more than 2-10 m. per secondat a temperature of zero degrees centigrade at a pressure of 760 mm. Hg,and relatively large thicknesses of contact layers of more than 15 mm.and preferably 20-50 mm. in thickness, a cooling medium of a constant ornearly constant boiling point can be used if the cross sections of thecontact layers perpendicular to the direction of the gas iiow in thedirection of the path of the gas through the contact are increased insize. The great thicknesses of the contact layers permit,

' at the same time, a simple construction of the apparatus ICE and acomparatively easy exchange of the contact. In the contact layers, whichlie at the gas entry and which have a smaller cross section than thosethat follow, the velocity of the gases is greater than in the laterones. The consequence is a greater heat transfer rate and, thus, abetter dissipation of the heat of reaction near the gas entry. Besides,here the heat transfer areas which enclose the catalyst are larger inproportion to the quantity of the catalyser than in the contact portionsfollowing, and thus effect an additional increase in the dissipation ofthe heat of reaction. On the other hand, the formation of heat for acertain specific catalysing eiect is smaller at the gas entry and nearthis point because of the small quantities of the catalyst present, andthe time of Contact of the reacting gas with the catalyst is shorter dueto the high velocity of the gas so that the synthesis of the gases andthe heat of reaction remain lower at this point than on the succeedingpassages of the gases through the catalyst. These conditions under whichthe reaction in the catalyser layer at the gas entry takes place resultin a small difference of temperature between the reacting gases and thecooling medium.

0n the succeeding path of the gas through the contact, on which thecross sections of the contact gradually or at intervals increase, thegas velocity and thus the rate of heat transfer decrease gradually, andthe heat eX- change surfaces which enclose the catalyser decrease inproportion to the quantity of the catalyser. Correspondingly, thedifference in temperature between the gas in the catalyser or thecatalyser space and the cooling medium increases gradually along thepath of the gas. With the temperature of the cooling medium remainingconstant, constantly increasing temperatures of reaction in thecatalyser are obtained. With increasing cross sections of the catalyserlayers the generation of heat at the catalyser increases further and thegas conversion is increased through the longer contact of the gas withthe catalyser, which result in a further steady increase of thetemperatures of reaction without requiring an analogous increase in thetemperature of the cooling medium.

The result ofthe increasing temperatures of reaction along the path ofthe gas is that the specific conversion of carbon monoxide and hydrogenis kept at a constant rate in all parts of the catalyser or can beregulated according to other requirements, thus eliminating the harmfuleffect which the decreasing concentration of carbon monoxide andhydrogen produces in the lower layers of the catalyser. lf, e. g. in adouble tube oven the distance between the inner tube and the outer tubeis increased from 10 mm. at the top of the oven to 25 mm. at the bottom,the temperature of reaction at a carbon monoxide-hydrogen conversionrate of 613%, increases approximately 15 or 20 during the passage of thegas from the top to the bottom through the contact. The Contact willwork faultlessly if the gas velocities are kept so high that due to theturbulent flow, a good dissipation of the heat of reaction and anequalization of temperatures in the contact is effected. In this processwater can be used as a cooling medium. Other fluids with a constantboiling point, such as diphenyl, diphenyl oxide,v

hydrocarbons, silicons, mercury and the like, may also be used. The newprocess can be applied with or without circulation of the reactinggases. The variation of the quantity of the circulating gas down toworking without any circulating gas offers the possibility to regulatethe change of the How velocity of the gases in the contact layer in thedirection of the gas flow in the most eiiiective manner, e. g., if alarger difference between the ilow velocity at the gas entrance and thegas egress is desired, one can work with small quantities or"circulating gas or without any circulation. In that case, the reactionproduces a strong contraction of the gas so that this contraction alsoproduces a decrease of the flow velocity and, thus, of the heat transferrate and a longer stay of the gas in the contact. Thus, through a changeof the circulating gas quantity, a change of the difference oftemperature between the entering and emerging gas is also obtained.

The heat transfer through the heat exchange surfaces may be furtherreduced in the lower part of the contact oven by providing for the heatexchange surfaces a material with a lower coefficient of heatconductivity or insulating material, e. g. incrustations at the heatexchange surfaces. One can also, as is well known, when using tube ordouble tube ovens, make the diameter of the tubes or the outer tubes inthe lower part of the oven larger than in the upper part.

The process according to the Vinvention permits the use of increasingtemperatures in the contact, independent of the direction of the gas ow.For instance, while passing the gases in the direction from the bottomto the top through the Contact, one can keep the temperatures at an eincreasing rate from the bottom to the top, but it is necessary to applythe methods described above, which produce these differences intemperature, in reverse, e. g. the cross sections of the contact layersmust increase in size from the bottom to the top while the gasvelocities and the specific size of the heat exchange surfaces must bereduced from the bottom toward the top. This possibility is ofimportance especially when working with catalysers kept in suspensionsince this process is applicable only when the gas flows from the bottomto the top.

The contact oven according to Fig. l consists of a pressure tank 1,which is provided with a top cover 2 and a bottom 3. The contact tubes 6are welded into the tube plates 4 and 5. The contact tubes 6 have on theinside concentrically arranged conical or graduated tubes 7, whosediameter decreases from the top to the bottom. The tubes 6 and 7 areconnected in such a manner that the cooling Water, which occupies thespace between the pressure tank 1 and the contact tube 6, can alsocirculate through the eoncentrically arranged inner tubes 7. Thecatalyser is placed in the annular space between the tubes 6 and 7 inlayers which increase in size toward the bottom. The gas to besynthesized enters into the contact oven through the upper sleeve 8 andis converted at the catalyser. As the layers increase in size, the gasvelocity decreases and the time of contact between the gas and thecatalyser increases, the temperature of reaction rises. The heat ofreaction is transferred to the boiling cooling water, the steamgenerated is carried o through the connecting pipe 9 and the steamaccumulator 10. The cooling medium circulates back into the contact oventhrough the connecting pipe 112 together with the water owing in throughthe pipe 11.

Fig. 2 illustrates another form of a contact tube. P1`hc contact tube1.3 consists of several pieces of tube 1.4, 1.5, 16 of differentdiameters and different lengths, which are welded together and, thus,have different cross sections of the layers.

Fig. '3 illustrates a Contact tube 17 in which the surfaces that carrythe heat off are varied by welded-on ribs 18 whose height decreasestoward the bottom and in this manner also effect a variation in thethickness of the layer.

Fig. 4 is a contact oven designed for working with suspended catalysers.It consists of a pressure tank 21 in which the catalyser is placed overthe grating 22. The gas to be synthesized enters the contact oventhrough the lower sleeve 23. The gas velocity is maintained high enoughto keep the catalyser in suspension. The gen'- erated heat of reactionis transferred to the boiling cooling water in the cooling tubes 24which extend into the catalyser space, and the steam generated iscarried ot through the collecting pipes 2S. rThe cooling tubes 24- areprovided with welded-on ribs whose height decreases from the bottomtoward the top. Through this arrangement, the heat transfer surface inthe lower part is increased and the thickness of the layer is decreasedso that increasing temperatures of reaction from the bottom toward thetop can be obtained.

The following examples are given by way of illustration and notlimitation:

Example l Hydrocarbon synthesis is carried out in a contact oven 3 m. indiameter and 1.5 m. high in which the catalysers are arranged stationaryin tubes. The contact oven contains 3100 tubes, each measuring 6 m.between top and bottom and having an inside diameter of 20 mm. at thetop which increases to an inside diameter of 40 mm. at the bottom. Thiscontact oven will take 15 m.3 of catalysts. The contact oven has acapacity of 15,000 Nm3 of the synthesis gas/hour under a pressure of 20atm. and of 37,500 Nm3/hour of return gas. The gas velocity, based onthe free cross section of the contact tubes and standard conditions (0and 760 mm. Hg), is 13.3 m./sec. in the contact tubes at the entry and3.55 rrr/sec. when leaving the oven. The heat transfer rate thusdecreases from 538 lf cal./m.2/hr./'J C. at the upper end of the oven to165 kcal./m.2/hr./ C. at the lower end of the oven while the heattransfer surface between the catalyser and the boiling cooling water,based on the same catalyser quantity, decreases by approximately 100%.With a temperature of 240 of the boiling cooling water surrounding theContact tubes, a temperature of reaction of 243 is observed where thegas enters the contact tubes, which by our invention increases to 263when the gas leaves the contact tubes. The production of hydrocarbons bythis contact oven is approximately 40 tons per day.

Example 2 A contact oven with contact tubes of 74 mm. inside diameter isused. Inside of these contact tubes there are concentrically arrangedtubes whose outside diameter of 44 mm. at the top is reduced to 24 mm.at the bottom. The heights of the layers in the contact tubes obtainedin this manner are 15 mm. at the top and 25 mm. at the bottom in theannular cross section perpendicular to the axis. 1070 contact tubes,each 6 m. high, are built into a contact oven which has a diameter of 3m. The contact oven holds 21 m.3 of the catalyser. It will be lled with21,000 Nm3/hour of synthesis gas under a pressure of 20 atm. and 52,500Nm3/hour of circulating gas. The gas velocity, with reference to thefree cross section of the contact tube, under standard conditions (0 and760 mm. Hg) is 7 m./sec. at thetop and diminishes to 5 m./sec. at thebottom. This reduces the heat transfer rate from 249 kcal./m.2/hour/ C.at the top of the oven to 139 kcal./m.2/hr./ C. at the bottom of theoven. The heat transfer surface diminishes by 17% from the top to thebottom while, under equal specific Contact loads, the heat generated atthe top is 40% 4less than at the bottom. At a .temperature of thecooling medium, boiling water, of 240, the temperature of reaction atthe oven entrance in the layers of l5 mm. thickness is 250 whichincreases to 265 at the oven exit with a thickness of the layer of 25mm. The yield of the contact oven is 58 tons of hydrocarbons per day.

Example 3 A contact oven with a diameter of 3.5 m. contains 5000 tubesof an inside diameter of 3l mm. and 10 m. in length, which have acapacity of about 46 m.3 of the catalyser. The contact oven is loadedwith 46,000 Nm3/hour of synthesis gas and with 115,000 Nm3/hour ofcirculating gas under a gas pressure of 20 atm. The outside of theContact tubes at the upper end is covered with an insulating layer of 1mm. in thickness. The insulatin:7 lay-er is enlarged toward the bottomandhas a thickness of 4 mm. at the lower end. Coatings of enamel,silicates or other insulating materials can `be used. The

prf

insulation can also be accomplished by placing another tube which isconically enlarged toward the bottom over tom. The annular space isconnected in one place with the gas space or the steam space of thecontact oven which forms the upper part of the'space for the coolingmedium. In this case, the gas space or the steam-filled annular space,whose inside diameter increases from 1 mm. to 4 mm.,makes theinsulation.

The heat transfer rate, which would amount to 444 kcal./m.2/hour/ C. ona non-insulated tube, is reduced by the insulation at the gas entry atthe top to 235 kcal./m.2/hour/ C. and by the stronger insulation at thegas exit at the bottom to 90 kcal./m.2/hr./ C. With a temperature of thecooling medium of 220, temperatures of reaction of 233 at the gas entryand 253 at the gas exit are obtained. With insulating layers made stillthicker, the temperature of the cooling medium may be further reducedeven at higher temperatures of reaction, the result of which is lowerpressures of the cooling medium if boiling water is used for cooling.The gas conversion amounts to 60% of the CO+H2 injected, and the yieldof the Contact oven is 90 tons of hydrocarbons per day.

Example 4 1200 double tubes, each m. long, are built into a contact ovenof a diameter of 3.5 m. Each double tube consists of an outside tubewith an inside diameter of 82.5 mm. and an inside tube, which has anoutside diameter of 30 mm. and is connected with the space containingthe cooling medium. 6 longitudinal ribs, 10 m. in length, are welded oneach inside tube distributed in equal distances from each other aroundthe perimeter. The height of the ribs is 26 mm. at the top where the gasenters and gradually decreases to 5 mm. at the bottom where the gaspasses out. The heat transfer area on the gas side is thereby reduced by50% from the gas entry to the gas exit. The contact capacity of the ovenis 53 m. With a load of 53,000 Nm.3/hour of synthesis gas under apressure of atm. and 53,000 Nm3/hour of circulation gas, at atemperature of 220 of the cooling medium,`the temperature of reaction atthe gas entry is 234 and at the gas egress 262. The yield of the contactoven is 100 tons of hydrocarbons per day.

l claim:

v1. In the production of hydrocarbons and hydrocarbon derivatives bycatalytic carbon monoxide hydrogenation, the improvement which comprisespassing synthesis gas at a velocity of at least about 0.5 meter persecond through a substantially confined longitudinally extending lixedbed `of particled catalyst of a cross-sectional mean bed thickness inexcess of 10 millimeters, and increasing from end to end in thedirection of gas flow, and cooling said catalyst with a coolant of asubstantially constant boiling point in substantially indirect heatexchange relation to the outside of said bed.

2. Improvement according to claim l in which said catalyst bed issubstantially vertically arranged and in which said synthesis gas ispassed substantially downwardly therethrough.

3. Improvement according to claim l in which said mean thickness is atleast 15 millimeters and in which said bed is defined by a substantiallycolumnar body of said catalyst.

4. Improvement according to claim 1 in which said mean thickness isabout 20 to 50 millimeters and in which said bed is defined by asubstantially columnar body of said catalyst.

5. Improvement according to claim 1 in which said synthesis gas ispassed at a velocity substantially between 2 and 20 meters per second.

6. Improvement according to claim l in which there is substantiallymaintained a temperature difference between catalyst and coolantsubstantially of about 10 to C. at the Widest catalyst bed section inheat exchange relation with said coolant.

References Cited in the le of this patent UNITED STATES PATENTS 857,389Ferguson lune 18, 1907v 2,181,927 Townsend Dec. 5, 1939 2,244,196Herbert lune 3, 1941 2,248,734 Barr June 8, 1941 2,255,126 MyddletonSept. 9, 1941 2,256,622 Murphree et al Sept. 23, 1941 2,353,600 SweetserJuly 11, 1944 2,475,025 Hutt July 5, 1949 2,481,089 Dickinson Sept. 6,1949 2,662,911 Dorschner et al Dec. 15, 1953

1. IN THE PRODUCTION OF HYDROCARBONS AND HYDROCARBON DERIVATIVES BYCATALYTIC CARBON MONOXIDE HYDROGENATION, THE IMPROVEMENT WHICH COMPRISESPASSING SYNTHESIS GAS AT A VELOCITY OF AT LEAST ABOUT 0.5 METER PERSECOND THROUGH A SUBSTANTIALLY CONFINED LONGITUDINALLY EXTENDING FIXEDBED OF PARTICLED CATALYST OF A CROSS-SECTIONAL MEAN BED THICKNESS INEXCESS OF 10 MILLIMETERS, AND